Onset of Knee Pain in OA Begins on Stairs

Up or down: stairs pose problems.

Action Points

In patients with knee osteoarthritis, pain on climbing stairs is the likeliest first symptom.

Pain during lying or sitting is less likely to have a mechanical origin.

In patients with knee osteoarthritis (OA), pain likely first appears during weight-bearing activities that involve bending of the knee, such as climbing stairs, a new study suggests.

The large observational analysis of people with confirmed radiographic knee OA, or those considered at high risk for this condition, found that of five activities that may result in mechanical loading on the knee joint, using stairs was most likely to be the first to cause pain, according to Elizabeth Hensor, PhD of the Leeds Institute of Rheumatic and Musculoskeletal Medicine at the University of Leeds, England.

This findings support the monitoring of patients for development of pain during activities to identify those with the first stages of OA who may benefit from early intervention, the researchers concluded in their paper appearing in Arthritis Care & Research.

The analysis included 4,674 patients from the Osteoarthritis Initiative (OAI), a multicenter, longitudinal prospective observational cohort (1,390 with confirmed radiographic OA, and 3,284 deemed at high risk of developing OA). Their mean age was 61.3 years and 58% were female.

Study participants completed the Western Ontario McMaster Universities Osteoarthritis Index (WOMAC) at baseline and annually up to 72 months. The WOMAC comprises subscales that measure stiffness, pain and function. Questions in the pain subscale relate to pain during five different activities: walking, using stairs, lying in bed at night, sitting/lying down, and standing. Each question has five possible responses -- none, mild, moderate, severe, and extreme -- which are scored from 0-4.

Researchers identified patients in the incidence cohort who scored 0 on the WOMAC at baseline and went on to score > 0 at a later time point. They selected the first knee to score > 0 and then calculated the proportions of patients affirming each item at the point of first scoring > 0. They restricted the analysis to patients who had affirmed just one item and assessed whether the five questions were equally likely to be affirmed first.

As the WOMAC has five response categories, there are four associated thresholds, which are points of transition on the logit scale (the scale expresses the trait value captured by an item).

"We sought to identify the item that contained the threshold with the lowest logit score of all, representing the point of transition from a total pain score of 0 to a score of > 0, i.e. the onset of knee pain," said the authors.

There were 550 patients in the incidence cohort with a complete set of WOMAC observations who scored 0 at baseline and went on to score > 0. At the point of scoring > 0, the proportions of patients affirming questions 1-5 were: 40% (walking), 81% (using stairs), 19%, (in bed), 21% (lying/sitting) and 27% (standing).

To further capture which WOMAC activity became painful first as the pain score increased from 0, researchers used a Rasch probability model. This analysis provides a means of formally assessing which question, and hence which activity, is associated with the transition point between the absence and presence of pain.

The analysis of a subset of 491 subjects showed a good fit with the Rasch model. The mean of the threshold locations for the question "pain on going up or down stairs" was considerably lower (-1.048) compared with "walking" (-0.054), "standing" (0.223), "lying/sitting" (0.54) and "in bed" (0.339).

This, said the authors, indicates that using stairs tended to be affirmed before the other activities. They noted that using stairs and walking are both weight bearing activities and involve knee bending while the other activities do not.

"Pain experienced while lying or sitting or while in bed, is perhaps less likely to have a mechanical origin," wrote the authors. "It is tempting to speculate as to whether pain during these activities might be the result of underling structural damage within the bone itself."

The authors concluded that prospective trials will help determine whether people who develop OA can be identified sooner if pain during weight-bearing activities involving bending of the knee is used during screening, perhaps facilitating effective intervention to prevent further disease progression.

A limitation of the study was the use of the WOMAC, which captures self-reported pain during activities rather than obtaining symptom measures related to performance-based testing. "Subjective interpretation of the questions could lead to variable results; however, pain will always be subjective irrespective of the nature of the associated activity," said the authors.

While another potential limitation was including individuals in the progression cohort in the Rasch analysis, the stairs item was consistently the first item to be affirmed irrespective of whether or not patients had radiographic OA.

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